Use of wet rubber masterbatch to improve filler dispersion characteristics and/or workability during manufacture of a rubber composition containing carbon black or other such filler has been known conventionally in the rubber industry. This involves causing filler and dispersion solvent to be mixed together in advance in a given ratio, causing rubber latex solution and a filler-containing slurry solution in which filler has been dispersed by means of mechanical force within dispersion solvent to be mixed together while in liquid phase, thereafter adding acid or other such coagulant, and collecting and drying the coagulum. As compared with use of dry rubber masterbatch obtained by causing filler and rubber to be mixed together while in solid phase, use of wet rubber masterbatch makes it possible to obtain a rubber composition having excellent filler dispersion characteristics and also having excellent workability as well as reinforcement characteristics and other such rubber properties. By using such a rubber composition as raw material, it is for example possible to manufacture rubber products such as pneumatic tires having reduced rolling resistance and excellent fatigue resistance.
Regarding methods for manufacturing wet rubber masterbatch, Patent Reference No. 1 describes a method in which a liquid mixture is prepared which contains natural rubber latex and a carbon black shiny that contains distilled water and carbon black dispersed within the distilled water, coagulation of the liquid mixture being carried out so as to obtain a granular coagulum.